Cavernous Maw is a uncommon Land — Cave card from The Lost Caverns of Ixalan (LCI), collector number 270. Current market price: $0.24 (foil $0.21), TCGplayer market prices via Scryfall.
{T}: Add {C}. {2}: This land becomes a 3/3 Elemental creature until end of turn. It's still a Cave land. Activate only if the number of other Caves you control plus the number of Cave cards in your graveyard is three or greater.